A coated cutting tool in which a TiN layer or a TiAlN layer, etc., has been formed on the surface of a substrate such as a cemented carbide, a cermet, a cBN sintered body, etc., has widely been used for cutting processing of steel, cast iron, stainless steel, a heat resistant alloy, etc.
As the conventional technique of a coated cutting tool, there is a surface coated hard member which comprises a base material such as a WC-based cemented carbide, a cermet, ceramics, a high speed steel, etc., and a coating film formed on the surface thereof and comprising a nitride, an oxide, a carbide, a carbonitride or a boride of an alloy which comprises 2 or more kinds of elements selected from Group IVa, Va and VIa metallic elements and Al and Si which has been constituted with a grain diameter of 50 nm or less by the physical vapor deposition method (for example, see Patent Literature 1.).
Also, there is disclosed that, in a hard film-coated tool in which a single layer hard film comprising either one of a composite nitride, a composite carbide or a composite carbonitride which mainly comprises Ti and Al, or a multilayer hard film comprising two or more kinds of the above is formed on the surface of a substrate, the hard film-coated tool comprises an average value of a crystal grain diameter (b) to a transverse direction of the hard film crystal grain being set in the range of 0.1 to 0.4 μm, and an average value of an aspect ratio a/b of the crystal grain diameter of the hard film being set in the range of 1.5 to 7 (for example, see Patent Literature 2.).